This invention relates generally to light attenuators and more particularly to electronically variable light attenuators.
As is known in the art, variable light attenuators are used in a wide variety of applications. One electronically variable light attenuator includes a polarizer, an electronic polarization rotator, and an analyzer. The light is first polarized by the polarizer to a particular orientation. The polarization rotator is adapted to rotate the polarization of the light passing through the rotator about the axis along which the light enters the attenuator. The analyzer is disposed in the path of the light exiting the rotator. Thus, for example, at one extreme, say when there is no voltage applied to the rotator, with the polarizer and the analyzer having the same polarization alignment, the light passes substantially unattentuated through the analyzer. At the other extreme, as when the polarizer rotates the polarization of the light entering it by ninety degrees relative to the analyzer, the light exiting the analyzer is substantially totally attenuated. An intermediate voltage will thus provide a degree of attenuation between these two extremes.
While such an arrangement may be useful in some applications, high-quality polarizers and attenuators having apertures of about one centimeter or larger are relatively expensive and have a relatively limited power handling capability.
In accordance with one feature of the invention, an electronically variable light attenuator is provided having an array of liquid crystal regions. The regions in a first set thereof are interspersed with the regions in a second set thereof. The array is adapted to receive a beam of light directed along an axis. A pair of electrodes is provided. At least one of the sets of regions is disposed between the pair of the electrodes. The regions in the first set are configured to produce a first diffraction pattern in response to the received light and the regions in the second set are configured to produce a second diffraction pattern in response to the received light. The pair of electrodes are arranged to enable the first and second diffraction patterns to combine with a degree of interference along an axis selected in accordance with an electric field produced through at least one of the sets liquid crystal regions disposed between the pair of electrodes.
With such an arrangement, a relatively low cost, high power electronically variable light attenuator is provided.
In accordance with another feature of the invention, the array degree of interference is greatest in the absence of the electric field.
With such an arrangement, a fail-safe attenuator is provided, because in the absence of a voltage between the electrodes the attenuator provides maximum attenuation. Such is desirable for example in a medical application where a laser light source is used during surgery. A power failure will, with such an attenuator, prevent high power laser light from impinging upon a patient.
In accordance with still another feature of the invention, the degree of interference is independent of the polarization of the received light.
With such an arrangement the requirement for costly polarizers or special laser axis requirement is eliminated.
In one embodiment, an electronically variable light attenuator is provided having an array of liquid crystal regions. The regions comprise a plurality of sets thereof, each one of the sets having a plurality of subsets of the regions, such subsets being interspersed within the set thereof. The array is adapted to receive a beam of light directed along an axis. A pair of electrodes is provided with at least one of the subsets of liquid crystal regions being disposed between the pair of electrodes. The regions in the subsets of each set thereof are configured to produce a corresponding diffraction pattern in response to the received light. The pair of electrodes are arranged to enable the corresponding diffraction pattern of the subsets to combine with a degree of interference along an axis selected in accordance with an electric field produced between the pair of electrodes.
With such embodiment, a relatively low cost and compact high power electronically variable light attenuator is provided.
In accordance with one embodiment of the invention, an electronically variable light attenuator is provided having an array of liquid crystal regions. The regions in a first set thereof are interspersed with the regions in a second set thereof. The array is adapted to receive a beam of light directed along an axis. A pair of electrodes is provided. At least one of the sets of liquid crystal regions is disposed between the electrodes. The regions in the first set are configured to produce a first diffraction pattern in response to the received light and the regions in the second set are configured to produce a second diffraction pattern in response to the received light. The pair of electrodes are arranged to enable the first and second diffraction patterns to combine with a degree of interference along an axis selected in accordance with an electric field produced through the at least one of the sets liquid crystal regions disposed between the pair of electrodes. The regions comprise liquid crystal molecules elongated along a director field axis. The director field axis of the molecules in the first set is orthogonal to the director field axis of the molecules in the second set.
In accordance with one feature, the projection of the director field axis of the molecules onto a plane orthogonal to the light propagation in the first set and the projection of the director field axis of the molecules onto the same plane in the second set are both orthogonal to the direction of the received light over a range of electric field strengths between the electrodes.
In accordance with another feature, the director field axis of the molecules in the first set of regions rotates in a first plane defined by an initial orientation and the light propagation direction as an electric field between the electrodes varies in strength and wherein the director field axis of the molecules in the second set of regions rotate in a second plane orthogonal to the first plane as the electric field between the electrodes varies in strength.
In accordance with one embodiment, at zero electric field, the regions in the first set provide an nxcfx80 phase shift to the received light relative to the phase shift provided to the received light by the regions in the second set, where n is an odd integer.
In accordance with one feature, the regions in the first set provide an nxcfx80 phase shift to the received light relative to the phase shift provided to the received light by the regions in the second set, where n is an odd integer in the absence of an electric field between the pair of electrodes for one polarization of the light, while at the same time the regions in the first set provide an xe2x80x94nxcfx80 phase shift to the received light relative to the phase shift provided to the received light by the regions in the second set in the absence of an electric field between the pair of electrodes for the orthogonal polarization of the light, where n is an odd integer.
In accordance with still another feature of the invention, a method is provided for electronically varying light attenuation. The method includes providing a pair of electrodes. The regions in a first set of liquid crystal regions are interspersed with a second set of liquid crystal regions. Both sets of liquid crystal regions are disposed between the pair of electrodes. The array is adapted to receive a beam of light directed along an axis. The regions in the first set are configured to produce a first diffraction pattern in response to the received light and the regions in the second set are configured to produce a second diffraction pattern in response to the received light. An electric field between the electrodes and through both sets of regions is varied producing the first and second diffraction patterns with a varying degree of interference along the axis.
In one embodiment, the array degree of interference produced is greatest in the absence of the electric field.
In one embodiment, the degree of interference produced is independent of the polarization of the received light. The regions are molecules having an elongated along a director field axis. The director field axis of the molecules in the first set is orthogonal to the director field axis of the molecules in the second set.
In accordance with yet another feature of the invention, a method is provided for electronically varying light attenuation. The method includes providing a pair of electrodes. A first set of liquid crystal regions is interspersed with the regions in a second set thereof. At least one of the sets of liquid crystal regions is disposed between the pair of electrodes. The array is adapted to receive a beam of light directed along an axis. The regions in the first set are configured to produce a first diffraction pattern in response to the received light and the regions in the second set are configured to produce a second diffraction pattern in response to the received light. An electric field between the electrodes and through the at least one of the sets of regions is varied producing the first and second diffraction patterns with a varying degree of interference along the axis. The regions are molecules having an elongated along a director field axis. The director field axis of the molecules in the first set rotates with respect to the stationary director field axis of the molecules in the second set.
In accordance with one embodiment, the director field axis of the molecules in the first set and the director field axis of the molecules in the second set are both oriented orthogonal to the direction of the received light. The director field axis of the molecules in the first set and the director field axis of the molecules in the second set are both oriented orthogonal to the direction of the received light over a range of electric field strengths between the electrodes.
In accordance with one embodiment, the regions in the first set provide an nxcfx80 phase shift to the received light relative to the phase shift provided to the received light by the regions in the second set, where n is an odd integer. The regions in the first set provide an nxcfx80 phase shift to the received light relative to the phase shift provided to the received light by the regions in the second set, where n is an odd integer in the absence of an electric field between the pair of electrodes.